The present invention relates to counterbalancing the weight of handheld implements thereby reducing the strain and physical fatigue resulting from the sustained use of implements such as weed cutters, hedge shearers, chain saws, Christmas tree shearers, pole pruners and other similar devices. The present invention makes it possible to increase the operating time and frequency of use of hand held implements as a direct result of decreasing the strain and fatigue associated with the operation of these implements.
Many implements have a weight of about 10 pounds and are suitable for short duration, occasional use; however, more frequent and extended usage of this equipment is tiring especially to the hands, arms and shoulders of the user. The extended and repeated use of these devices may contribute to repetitive motion or stress injury such as carpal tunnel syndrome.
The present invention is useful in suspending and supporting the implement and allowing all the motions required to use the implement while nearly eliminating its handheld weight through the use of a counterbalancing system which supports, and transfers nearly all weight, usually supported by the operators hands and arms, to a body harness which is primarily supported and fastened at the operators waist along with secondary support and fastening to the operators upper torso.
The need to support heavy objects which are not readily carried by a person is well known. The backpack has been shown to result in decreasing the effort and increasing the efficiency of carrying loads compared to carrying by hand. The backpack, especially the improved modern versions, has been used to support, suspend and carry loads which sometime exceed 100 pounds although recommended loads are usually one third of the body weight of the individual.
Ancient stationary devices such as the sweep have been used to at least partially counterbalance loads, usually ground water, which is raised manually using a rope attached to one end of a boom which is pivoted above a vertical ground anchored post or mast.
The manufacturing industry has made use of counterbalancing booms to vertically support tools which are used in production . One such mechanism is described in U.S. Pat. No. 5,213,292, issued to Maurice Evans on May 25, 1993. The mechanism disclosed has a swing arm mounted at one end to a fixed column with an articulating arm pivotally mounted at the opposite end of the swing arm. A tool holder is mounted at the distal end of the articulating arm. Springs connected to and extending above the articulating arm counterbalance both the articulating arm and an attached tool holder using a unique method of adjusting the spring tension for use with tools having different weight. This device is satisfactory for manufacturing and assembly work where a permanently anchored, stationary, sturdy and heavy column is available. There is no suggestion or teaching of adapting this device for portable use. Also a large unidirectional bending moment is produced at the column resulting from the weight and position of the entire mechanism including the spring itself making this device unsuitable for portable use.
Another fixed support system has a curved overhead boom rigidly connected to a back pack, extending upward and forward passing overhead and in front of the user. This device has no known patent number but is made by Saje ( registered trademark), a maker of shearing machines for trees. This xe2x80x9ccustom fitxe2x80x9d backpack has a rigid boom having an attached strap which hangs from the extended end of the boom directly in front of the users head for attachment and support of a power driven shearing bar held by the user. This system supports the weight of the shearing bar and allows limited movement fore and aft and left and right due to movement of the short strap; however, the boom is rigid and provides vertical support but does not provide counterbalancing during vertical motion. The attachment strap allows only limited pitch and yaw and provides for only limited rotation.
Another commonly used support for weed-cutters is the over the shoulder sling with an attachment clip which is used to connect the implement at a level near the users waist. This arrangement provides pivotal support at the point of connection: to the implement and allows the implement to be moved in a arcuate pattern but does not provide counterbalancing when the implement is lifted vertically. The sling restricts and impedes movement to the left, right, fore and aft and provides for only limited rotation.
Aspects of the present invention provide a compliant body harness which is integrally connected to a counterbalancing system which provides vertical counterbalancing over an extended range of vertical motion while allowing a full range of implement manipulation. Counterbalancing is done using a pivotal boom assembly, located over the implement, having a flexible rope or cable connecting the implement to the end of the boom.
The counterbalancing system is arranged so that the lifting support it provides to the implement is nearly vertical and above the implement especially while lifting and extending the implement in the forward direction due to the arcuate movement of the pivoting boom complimenting the arcuate movement of the users arms pivoting about the users shoulders.
Pitch, yaw and rotational movements of the implement are made possible due to a pivotal connection of the implement at the end of the rope and the compliant characteristics of the rope itself. The extended rope allows the implement to be moved fore and aft, as viewed from the operators perspective, as well as left and right and a compliant body harnessing arrangement provides additional movement thereby allowing a complete range of implement movement.
The described combination forms a portable counterbalancing system suitable for supporting devices such as tree shearers, weed-cutters, pole pruners, chain saws as well as other devices. The counterbalancing system, which uses springs to provide the counterbalancing force, reduces the hand held weight of a 10 pound implement to typically no more than 5 percent of the implements weight over the entire operating range of motion which the implement is used. This is accomplished by efficiently transferring approximately 95 percent of the implement weight to the body harness by using an integrally connected counterbalance. Since the implement is held in front of the user, the counterbalance is arranged so that most of the operating mechanism, such as the extension springs used to provide the counterbalancing force, is located behind the user to minimize back rest pressure and force and to transfer as much weight as possible to the users waist. If the spring were located in front of and above the user the springs weight would result in an increased moment which would impose more back rest force against the users back.
A typical overall weight of the described counterbalancing system, including the body harness, is about 5 pounds. This system will result in a hand held weight of no more than xc2xd pound when used to counterbalance a 10 pound implement over a range of vertical motion of 60 inches. The described system would be said to be under-balanced by xc2xd pound. This system also allows for over-balancing. An over-balanced condition could be adjusted or set, by altering the spring force, to provide an excess lifting force of 12 ounces with no lifting required by the hands to raise the implement. A condition such as this would require downward hand force to maintain equilibrium but when used for above-the-shoulder lifting would partially compensate for the weight of the users arms thereby reducing the overall operating effort.
The operating characteristics of the device do not result in exact counterbalancing throughout the entire vertical operating range and about 3 ounces of friction is typical. However, proper design and spring adjustment results in near perfect counterbalancing at two positions over the entire operating range with a few ounces of both under-balancing and over-balancing present throughout the remainder of the vertical operating range.